One of the advantages that certain medical imaging techniques, such as diagnostic ultrasound imaging, has over many other diagnostic imaging modalities is the ability to produce realtime images. This advantage has been especially significant in echocardiography where the physiology of a continually moving organ, i.e. the heart, is the subject of study. Realtime imaging has been a virtual necessity in echocardiography, as compared with abdominal and obstetrical applications where the tissues and organs being studied are stationary and may be readily examined by static imaging.
A wide range of cardiac studies can be performed using recorded, realtime moving images, and qualitative review of such images by trained medical personnel can detect congenital heart defects, large aneurysms or stenoses in the major coronary arteries, and other gross anatomical abnormalities. Analyses such as heart pumping capacity measurements, wall motion abnormalities blood perfusion studies in the myocardium and coronary vessel tracking provide complementary quantitive diagnostic information.
One major problem in evaluating, for example, cardiac structures from two- and three-dimensional data has been to ensure that one is observing the same tissue or structure as the heart moves through the cardiac cycle. What is desired is a consistent view of the tissue structure throughout the cardiac cycle, even though the structure is moving along with the rest of the heart. For example, when observing the mitral valve annulus, left ventricular outflow tract or a short-axis view of the left ventricle at a particular level, a plane defining an MPR slice or oriented 3D view of the structure is currently defined using the frame of reference of the image acquisition. However, because the structure of interest is moving relative to the imaging frame of reference, along with the rest of the tissue, it may pass into and out of the view, which has the effect of complicating the process of evaluating the structure. This is one reason why it took many years to appreciate the saddle shape of the mitral annulus, for example.